In a multimedia system, the device presenting content to an end-user must be provided with a technique for determining which services are available, and how to present individual services when they are selected. In the early days of television, the list of available services was predefined; there were twelve bands on which television signals could be communicated, and the client could select any one of them. Metadata about content actually being carried on the channels was delivered “out of band,” in the form of newspaper listings or television guide magazines. A similar set-up applied to radio broadcasts.
As television migrated to digital delivery, content-delivery techniques became more complicated, as multiple services could be multiplexed within an individual band. When MPEG transport streams were invented, the designers included an information standard for grouping and selecting content from a multiplexed stream, known as “system information” or simply SI. The MPEG SI describes which audio stream and video streams to combine to create a service, and indicates to the client where each can be discovered. Still, metadata describing the content actually being displayed on a particular service at a particular time was delivered out of band. Even contemporary on-screen electronic program guides get their data from out of band sources.
Another example of a standard designed to carry acquisition information is the digital video broadcasting (DVB) family of standards, which describe a system for carrying MPEG transport streams over the air or from satellite. Although these forms of MPEG SI are extremely useful for describing the contents and properties of an MPEG transport stream, they are not capable of carrying information about more general types of content (web pages, flash animations, and so on).
The first generation of digital media devices had to be constructed with specialized hardware, because it was simply not cost-effective to use a general-purpose computer to perform multimedia tasks. As a result, set top boxes were generally designed to target a particular mode of data delivery and a particular type of data content. For example, the first generation of the MOTOROLA DCT family of cable set top boxes was originally designed to exclusively display analog and MPEG video content. Similarly, the original generation of digital satellite receivers simply consumed MPEG transport streams from a satellite and displayed them. Both of these types of devices had extra user interfaces (UIs) for displaying guide metadata and offering pay-per-view content, but there was no provision for a more universal, general schema to direct content of different service types to the box, because at the time there was no way to make use of other types of content besides analog and MPEG video.
Some current multimedia systems use Internet protocols to distribute data. The number of different types of data which can potentially be acquired by the client is limited only by the capacity of the client to acquire, recognize, and properly process the content. Beyond just being able to decode different types of content (for example, MICROSOFT® WINDOWS® media versus MPEG media), some of the systems can use multimedia content delivered in various different manners (for example, WINDOWS® streaming media carrying live channels; WINDOWS® media carried in on-demand servers for providing movies; media played back from a local, attached hard drive, etc.). This flexibility requires a different system from the ones used in a conventional unidirectional approach.
Another aspect of using Internet protocols to distribute multimedia data is that individual end-users may contribute data to the network (e.g., upload content or send content horizontally to end-user peers) in addition to simply consuming programs in a downstream direction from the commercial service provider. In a model similar to those described above, if the Smiths create their own slide-show, digital music, or home movie and wish to deliver it to their friends for consumption on their home multimedia display system, the Smiths would be required to provide SI data to the central service provider, which would then be re-distributed from the central provider to the friends. This is inefficient and non-user-friendly, and there is no vehicle for associating metadata with the uploaded content so that end-recipients can see a description before playing the content. That is, the traditional metadata distribution techniques are also centralized and unidirectional, and typically focused on delivering descriptions of on-demand movies and live television content. Consumers are increasingly able to produce and host their own content for delivery to fellow consumers. Additionally, a whole universe of third-party commercial content providers vie to provide content to consumers. A way is needed to signal metadata and transfer acquisition information so that content from many diverse sources can be integrated into a unified user experience that does not rely on centralized distribution, or on being embedded with a particular media stream.